It has been estimated that there may be as many as 1 million different fungal species on our planet (Hawksworth, D. C. and A. Y. Rossman, A. Y., 1987. “Where are the undescribed fungi?”, Phytopath. 87, 888-891). In the past century, many of the 0.1 million fungi that have been described have been those associated with various higher organisms as either parasites or saprophytes on dead and dying biological materials. Thus, the question, where are the remaining 0.9 million fungi? It turns out that microorganisms seem to occupy virtually every living and non-living niche on earth. This includes those in the thermal vents, in deep rock sediments, and in desert as well as marine environments.
In the past few decades, plant scientists have begun to realize that plants may be serving as a reservoir of untold numbers of organisms known as endophytes (Bacon, C. W., and White, J. F. 2000. Microbial Endophytes. Marcel Deker Inc., N.Y.). Endophytic fungi and bacteria are those organisms living within the tissues of host plants. By definition, these microorganisms (mostly fungi and bacteria) live in the intercellular spaces of plant tissues. Typically, endophytes coexist with their hosts without any pathogenic symptoms. These organisms have proven to be an unusually rich source of novel bioactive natural products.
Some of these endophytes may be producing bioactive substances that, in some way may be involved in the host—endophyte relationship. As a direct result of the role that these secondary metabolites may play in nature, they may ultimately be shown to have applicability in medicine, agriculture and industry. We are now witnessing the beginning a worldwide scientific effort to isolate endophytes and study their natural products. While there are many epiphytic microorganisms associated with plants, the endophytic associations may be more complex since living host tissues are involved. This may be the case since closer biological associations may have developed between these organisms in their respective hosts than the epiphytes or soil related organisms. Hence, the result of this may be the production of a greater number and diversity of classes of biological derived molecules possessing a range of biological activities. In fact, a recent comprehensive study has indicated that 51% of biologically active substances isolated from endophytic fungi were previously unknown (Schutz, B. 2001. British Mycological Society, International Symposium Proceedings, Bioactive Fungal Metabolites-Impact and Exploitation. University of Wales, April). This compares with only 38% novel substances from soil microflora.
One of the least studied biochemical-chemical systems in nature is the relationship existing between microorganisms and their plant hosts. For instance, it does appear that all higher plants are hosts to one or more endophytic microbes. These microbes include the fungi, bacteria and actinomycetes. They reside in the tissues beneath the epidermal cell layers. It is well understood that endophytic infections are at least inconspicuous (Bacon, C. W., and White, J. F. 2000. Microbial Endophytes. Marcel Deker Inc., N.Y.). And as a result, the host tissues are transiently symptomless and the colonization of the tissues is internal to the surface of the plant. The exact physical relationship of the endophyte to the plant has, in most cases remained obscure, because it is extremely difficult, by electron microscopic techniques, to find an endophyte within plant tissues. Conceivably, the microbes live within the intercellular spaces of the tissues and it also seems likely that penetration of living cells may occur but not easy to observe. The relationship that any given endophyte establishes with the plant varies from symbiotic to that bordering on pathogenic.
It also turns out that these relationships may have begun to evolve from the time that higher plants first appeared on the earth hundreds of millions years ago. Evidence of plant associated microbes has been discovered in the fossilized tissues of stems and leaves (Bacon, C. W., and White, J. F. 2000. Microbial Endophytes. Marcel Deker Inc., N.Y.). As a result of these long held associations, it is possible to imagine that some of these endophytic microbes may have devised genetic systems allowing for the transfer of information between themselves and the higher plant and visa versa. Obviously, this would permit a more rapid and reliable mechanism of the endophyte to deal with ever changing environmental conditions and perhaps allow for more compatibility with the plant host. In addition, independent evolution of the endophytic microbes may have allowed them to better adapt to a plant host and perhaps develop to a point where they could contribute to their relationship to their host plant by carrying out such functions as protection from pathogens, insects, and other grazing animals. Or in still another case, it is possible to imagine that certain products from the endophyte may protect the plant from the harmful effects of irradiation, oxidation, and other events that occur as a natural consequence on living on this earth.
Recently, we described two novel endophytic fungi, Muscodor albus from Cinnamomum zeylanicum from Honduras (Worapong et al., 2001), and M. roseus from two monsoonal rainforest trees in Northern Australia (Worapong et al., 2002). These endophytes produce a mixture of volatile antimicrobials that effectively inhibit and kill a wide spectrum of plant-associated fungi and bacteria (Strobel et al., 2001). On the other hand, the gases of M. albus did not kill fungi that were related to it, some of which were producers of other lethal gas mixtures (Worapong et al., 2001 and Worapong et al., 2002).
Accordingly, it is an object of the present invention to provide additional Muscodor species that have biological activity.